Barrier layers are used in electronic devices such as semiconducting devices, printed circuit boards, IC substrates and the like to separate layers of different composition and thereby prevent undesired diffusion between such layers of different composition.
Typical barrier layer materials are binary nickel alloys such as Ni—P alloys which are usually deposited by electroless plating onto a first layer of a first composition followed by deposition of a second layer of a second composition onto the barrier layer. Such first layer can consist of copper or aluminium.
Another application of barrier layer materials in electronic devices is as a cap layer which is e.g. deposited onto copper to prevent corrosion of copper.
Another application of nickel and nickel alloy deposits is corrosion protection for various substrates.
Compositions for electroless nickel plating solutions are known in the art. For example, U.S. Pat. No. 2,658,841 teaches the use of soluble organic acid salts as buffers for electroless nickel plating solutions. U.S. Pat. No. 2,658,842 teaches the use of short chain, dicarboxylic acids as exaltants to EN baths. U.S. Pat. No. 2,762,723 teaches the use of sulfide and sulfur bearing additives to an electroless nickel plating bath for improved bath stability.
U.S. Pat. No. 2,847,327 has introduced other means of stabilizing an electroless nickel plating solution. These include the use of higher purity starting materials; more effective stabilizers from the class of heavy metals such as Pb, Sb, Bi, Cu and Se; inorganic compounds such as iodates, and thio compounds; organic compounds such as unsaturated alkenes and alkynes and others.